Method for embossing webs

ABSTRACT

Embossing a web between unmatched male and female embossing elements, wherein the sidewall slope of the female element is different than the sidewall slope of the male element, provides an embossed web having markedly improved embossing pattern definition and, in the case of roll products, greater roll bulk at equivalent roll firmness. The unmatched male and female embossing elements are preferably made by laser engraving rubber embossing rolls.

This is a divisional application of application Ser. No. 07/870,528,filed on Apr. 17, 1992, still pending which is a continuation in part ofSer. No. 07/660,317filed Feb. 22, 1991, now abandoned.

BACKGROUND OF THE INVENTION

In the manufacture of tissue products such as facial tissue, bath tissueand paper towels, it is known that embossing increases the bulk of theproduct as well as improves aesthetic appeal. A trade-off, however, isthe fact that embossing also reduces the strength of the embossed sheetand, in the case of roll products, an increase in bulk is accompanied bya decrease in roll firmness.

SUMMARY OF THE INVENTION

It has now been discovered that male and female embossing elementshaving different geometries (unmatched embossing elements) and which arepreferably made of a relatively deformable material such as rubber orplastic can produce a visually more distinct embossing pattern whichimparts-greater bulk to the embossed sheet with substantially less lossof firmness compared to conventional embossing techniques. Suchdifferences in geometry create "pinch points" as the male and femaleembossing elements are engaged where the web to be embossed iscompressed or pinched between a sidewall of the female embossing elementand a bottom corner of the male embossing element and/or is compressedbetween a sidewall of the male embossing element and the top edge of thefemale embossing element. It is believed that the pinch points causeisolated compressions of the web which impart durability to theembossments. This results in embossments which are more distinct thanconventional embossments and provides greater bulk at a given level offirmness. For purposes herein, embossing elements are protrusions (maleembossing elements) or depressions (female embossing elements) formed onthe surface of a roll or plate used for creating correspondingdeflections (embossments) in a web. Common methods of forming embossingelements include engraving or etching.

Hence in one aspect, the invention resides in a method for embossing aweb comprising deflecting the web between unmatched male and femaleembossing elements, wherein the slope of at least one sidewall of thefemale embossing elements is different than the slope of thecorresponding sidewall of the male embossing elements.

In another aspect, the invention resides in a pair of embossing rollshaving unmatched male and female embossing elements, wherein the slopeof at least one sidewall of the female embossing elements is differentthan the slope of the corresponding sidewall of the male elements. Thepair of embossing rolls can include one roll having all male elementsand the second roll having all female elements, or each roll can haveboth male and female elements. Preferably at least one of the embossingrolls, and most preferably both of the embossing rolls, is covered witha rubber surface. Rubber embossing elements yield slightly to the weband are believed to be less likely to damage the strength of the webduring embossing.

In a further aspect, the invention resides in an embossed web producedby the methods described herein.

More particularly, the invention resides in a creped bath or toilettissue having a sheet bulk/embossed area ratio of about 50 or greater,more preferably about 60 or greater, and most preferably about 75 orgreater, wherein sheet bulk is expressed as cubic centimeters per gramand embossed area is expressed as the fraction of the surface area whichhas been deflected inwardly from the outside of the tissue web.Preferably, such bath tissues have a sheet bulk of about 12 cubiccentimeters per gram or greater, more preferably about 13 or 14 cubiccentimeters per gram or greater.

Sheet bulk is measured substantially in accordance with TAPPI StandardT411-68 except for the loading on the pressure foot, which is 95 gramsper square inch. The method utilizes a TMI Bench Micrometer, Model549MSP having a 2 inches diameter anvil, and comprises placing a singlesheet of tissue on the anvil such that all points on the peripheries ofthe contact surfaces are at least 1/4 inch in from the edges of thesample. The instrument motor is started and two measurements are takenwithin 6 inches of each other in the cross-machine direction of thesample. A reading is taken near the end of the dwell time on each testand is read to the nearest scale division. The average of the tworeadings is the sheet bulk of the tissue.

The embossed area of the tissue is determined by simply filling in theembossing depressions in the tissue with a black pen and using standardimage analysis practices to measure the percent area of the tissue whichhas been darkened with the pen. More particularly, one sheet of bathroomtissue is removed from the roll and placed on a table with the tissuesurface from the outside of the roll facing up. All of the embossingdepressions or channels of the tissue sheet are darkened using aBIC.sup.® Micro Metal black ink pen. Care should be taken to only darkenin the indented portions of the sample as accurately as possible. Themarked tissue sheet is then subjected to image analysis by placing thetissue sheet on a uniformly well lighted table. A camera (Dage MTI CCDVideo CameraModel #VE CCD) and lens assembly (Nikkon 28-85 mm zoom) aremounted on an adjustable overhead stand with the camera lens pointeddownward at the sample. The tissue is brought into focus so that theentire screen is filled with the embossed sample to be examined. Theimage is aquired into an image analysis system (Sun Spark Station 1 withPGT Imex System Feature Analysis Software) and a detection threshold isset. The image is binarized and the field is examined for total embossed(black) area, which is expressed as a decimal fraction between 0 and 1.

As indicated above, a feature of this invention pertains to therequirement that the male and female embossing elements are "unmatched".As used herein, this term is intended to mean that the male and femaleembossing elements are not identical in shape, but still are positionedrelative to each other in registry such that they engage. This is meantto distinguish from conventional "matched" steel embossing elements inwhich the male elements are engraved first and the female elements aresubsequently made from the male elements, or vice versa, so that bothelements are virtually inverse or reciprocal images of each other withinthe practicalities of manufacturing tolerances. This is not the casewith the embossing elements of this invention, wherein although the maleand female elements fit together or engage reasonably well, the sidewallslopes of the male and female embossing elements differ sufficiently toprovide differential compression and/or shear on certain portions of theweb when the embossing elements are engaged, meaning that all portionsof the web which form an embossment sidewall are not compressed and/orsheared the same. This differential compression occurs when a sidewallof the male embossing element approaches contact with an upper corner ofthe female embossing element and/or a sidewall of the female embossingelement approaches contact with a bottom corner of the male embossingelement. Both conditions can occur simultaneously in the samemale/female embossing element pair.

It is preferable that the slope of the male element sidewall be fromabout 5° to about 85° , and more preferably from about 50° to about 70°or greater. It is believed that steeper sidewall angles create a morepermanent kink in the web in the vicinity where the embossment meets theundeflected area of the web when the slope of the male element sidewallis less than the slope of the female element sidewall. Because the depthof the resulting embossment is, determined by the extent to which themale embossing element penetrates the female embossing element, in thisembodiment of the invention the difference in sidewall slopes should notbe so great that the penetration or degree of engagement of the maleembossing element is insufficient to achieve the desired bulk. Althoughthe degree of difference between the sidewall slope of the male andfemale elements can vary, it is preferred that the sidewall slope of themale element be at least about 2° greater or less than the correspondingslope of the female element, and more preferably from about 5° to about10° greater or less than the corresponding slope of the female element.For purposes herein, the sidewall slope is measured relative to theplane of the undeflected web during embossing, with the maximum slopebeing perpendicular (90°) to the undeflected web. This is described ingreater detail below with regard to FIG. 3.

It must be kept in mind that the practicalities of commercial engravinglimit the ability to make embossing rolls in which the male and femaleembossing elements contact each other in the same manner everywhere onthe embossing roll or plate. When viewing embossing element engagementin two dimensions (cross-sectional photographs), some embossing elementswill be shown to contact each other on both sides as hereinafterillustrated in FIG. 3. In other instances, some embossing elements willbe shown to contact each other only on one side. In still other areas,the embossing elements may appear to not touch at all. However, overall(over the entire embossed sheet surface) there are a sufficient andsubstantial number of pinch points to impart exceptional bulk andfirmness to the web and integrity to the embossments. The varyingdegrees of engagement exhibited by the male and female embossingelements in accordance with this invention will be further illustratedand discussed in connection with FIG. 4.

When manufacturing embossing rolls for use in connection with thisinvention, laser engraving is a preferred method of manufacture becauseof its precision and lower cost. Laser engraved rubber sleeves forembossing rolls and laser engraved plates are commercially availablefrom Midwest Rubber Plate Co., Menasha, Wis. The material of the maleand female embossing elements is preferably a deformable material suchas rubber, plastic or the like. Such materials are not only moreforgiving with respect to degrading the strength of the web duringembossing, but they also are suitable for laser engraving. As usedherein, "rubber" is meant to include any relatively deformable materialhaving a Shore A hardness of about 100 or less and preferably about 90or less. Other suitable deformable materials include nylon, polyesters,polyurethane, polytetrafluoroethylene (Teflon), poly(vinyl idenefluoride co hexafluoropropylene) (Viton), and the like.

Although deformable embossing element materials are preferred, it isalso within the scope of certain aspects of this invention for theembossing elements to be steel or combinations of steel and rubber orother deformable materials. For example, the male elements can be steeland the female elements can be a deformable material, such as rubber, orvice versa. It will be appreciated that many different suitablecombinations of materials are possible and within the scope of thisinvention. The steel rolls of this invention can also be used forbonding nonwovens by heating the rolls to provide a unique bondingpattern.

The web to be embossed in accordance with this invention can be any websuitable for embossing, including paper, tissue, nonwovens, films,laminates, combinations thereof and the like. The webs can be preheatedor premoistened. In the case of tissue webs, which for purposes hereinmeans webs intended for use as facial tissue, bath tissue, table napkinsand paper towels, the web can be layered or nonlayered, creped oruncreped, wet pressed or throughdried, single-ply or two-ply or multipleply, and can comprise natural and/or synthetic fibers. Creped tissuewebs are preferred, which have a finished dry basis weight of from about5 to about 40 pounds per 2880 square feet per ply and a geometric meantensile strength of from about 300 to about 12,000 grams per 3 inches ofwidth.

For purposes herein, roll bulk is the volume of a product (in cubiccentimeters) divided by the weight of the product (ingrams). For rollproducts such as bath tissue and paper towels which have a hollow core,the product volume "V" is calculated as follows:

    V=π(R.sub.1.sup.2 -R.sub.2.sup.2)W

wherein

R₁ =radius of the roll;

R₂ =outside radius of the hollow core; and

W=width of the roll.

For a rectangular stack of product such as facial tissue, the productvolume is simply the length×height×width of the stack.

The Firmness Index is a measure of the distance, expressed in inches,that a weighted probe deflects the surface of a roll or stack ofproduct. A greater deflection distance and hence a greater FirmnessIndex reflects lesser product firmness. The method and apparatus formeasuring the Firmness Index will be described hereinafter in connectionwith the detailed description of FIGS. 7 and 8.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of prior art embossing using matchedsteel embossing elements.

FIG. 2 is a schematic illustration of prior art embossing using steelembossing elements against a rubber roll.

FIGS. 3A and 3B are schematic illustrations of an embossing method in,accordance with this invention and the resulting embossed product.

FIGS. 4A, 4B, and 4C are cross-sectional photographs of a tissue webbeing embossed between male and female embossing elements in accordancewith this invention, illustrating the varying degrees of contact betweenthe male and female elements which can occur within the same embossingpattern.

FIGS. 5A and 5B are cross-sectional photographs comparing a conventionalembossed tissue web and a web in accordance with this invention,respectively.

FIG. 6 is an illustration of the apparatus used to measure the FirmnessIndex for roll products such as bath tissue and paper towels.

FIG. 7 is an illustration of essentially the same apparatus illustratedin FIG. 6, but modified slightly to measure the Firmness Index ofstacked products such as facial tissue and table napkins.

FIGS. 8A and 8B are plots of roll bulk vs. roll Firmness Index forembossed bath tissue of this invention compared to the same tissuesembossed using matched steel rolls.

FIG. 9 represents the particular embossing pattern referred to in thedescription of the previous Figures.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing, the invention will be described in greaterdetail.

FIG. 1 illustrates an embossing process of the prior art in which atissue web is embossed between matched steel embossing elements. Shownis a male steel embossing element 1 and a matching female steelembossing element 2 in an engaged position. The web 3 being embossed isdeflected between the embossing elements as shown. The amount of webcompression is greatest between the male embossing element sidewalls 4and the female embossing element sidewalls 5. Because the sidewall slopeof the matched steel male and female embossing elements is identical,the extent of web compression is substantially uniform at all pointsbetween the bottom edge 6 of the male element and the top edge 7 of thefemale element. Under typical embossing conditions, the web isrelatively uncompressed in the region between the bottom 8 of the maleelement and the bottom 9 of the female element.

FIG. 2 illustrates another embossing process of the prior art wherein atissue web 3 is embossed between a male steel embossing element 1 and arubber embossing surface 11 which partially conforms to the steel maleelement when engaged as shown. In this type of embossing process, thegreatest degree of web compression occurs between the bottom 8 of thesteel element and the corresponding surface 12 of the rubber. In thearea of the male element sidewalls 4, there is a gradual increase in webcompression from a point 13 on the undeflected surface of the rubber toa point 14 near the bottom edge 6 of the male element.

FIG. 3A illustrates a preferred embossing method of this invention inwhich a tissue web 3 is deflected between a male embossing element 31and an unmatched female embossing element 32. FIG. 3B illustrates theresulting embossment 33 of the embossed product. Unlike the prior artembossing methods illustrated in FIGS. 1 and 2, the greatest degree ofweb compression and/or shear in the method of this embodiment of theinvention occurs in the circled areas 34 located in the vicinity of thetop edge of the female element. This occurs because in this embodimentthe sidewall slope of the female element sidewall 35 is greater than thesidewall slope of the male element sidewall 36. It is theorized thatapplying maximum compression and/or shear only at the edge of theembossment realigns or deforms the fibers in this area in such a mannerto give the resulting embossment greater structural integrity. In effecta more permanent crease or bend is imparted to the web at the edge ofthe embossment which results in greater embossment distinctness and agreater firmness retention for the embossed web. As previouslydescribed, the sidewall slopes are measured relative to the plane of theundeflected web as indicated by dashed line 37. The sidewall slope ofthe male embossing element as shown in FIG. 3A is indicated by the anglerepresented by the double arrow 38. The sidewall slope of the femaleembossing element is the angle represented by the double arrow 39. It ispreferred that the male and female embossing elements are both made ofrubber or other resilient material to provide an embossing surface whichis more forgiving than steel and is less likely to cut the web at thepoint of near contact between the male and female embossing elements.

FIG. 3B also illustrates the maximum angle of deformation exhibited bythe embossment 33. Shown is the undeflected plane of the web 37 and aline 40 which is aligned parallel with the centerline of the embossmentsidewall to give the greatest value for the angle represented by thedouble arrow 41. Determination of the maximum angle of deformation canreadily be done with the naked eye by using a representativecross-sectional photograph of the product

However, the maximum angle of deflection can also be calculated usingimage analysis procedures. One method to accomplish this is to input thecross-sectional photograph into an image analyzer with the generalcenter of the cross-section running in the horizontal, or x, direction.The computer image is corrected for shading differences and then isdiscriminated to create a binary image in which the tissue component isdetected. Next, the binary image is manually edited to remove any grosssmudges appearing in areas outside of the tissue component. A series ofdilations is performed to fill in void areas of the tissue image. Then,an opposite set of erosions is performed to maintain the tissue sheet'scontour. Finally, the resulting tissue image is skeletonized to a lineof pixtels. Precautions must be taken to preserve line endpoints duringskeletonization. The image that results from this step is equivalent toa line drawn through the center of the tissue cross-section. Once theskeletonized image is obtained, it may be broken up into line segments.Typically, 32 line segments are created across the y-direction of theimage. The angle of the individual line segments is easily measured asthe inverse tangent of the ratio of Feret Y or Feret X. The maximumangle of the line segments is a measure of the steepness of theembossment sidewall.

FIGS. 4A, 4B and 4C are cross-sectional photographs (magnified 25×) of acreped tissue web being embossed between unmatched, laser engraved,rubber embossing elements in accordance with this, invention. Theembossing pattern was that as illustrated in FIG. 9. The cross-sectionsare taken at different positions of an embossing element to illustratethe manner in which the web is acted upon by the embossing elements ingeneral and the variation in the manner in which the embossing elementsengage. The particular embossing elements illustrated were from rubbersleeves adapted to be used on embossing rolls. The dimensions of themale embossing elements, in inches, were 0.060 in depth, 0.085 wide atthe top, and 0.025 wide at the bottom. The sidewall slope of the maleembossing elements was about 60° . The dimensions of the femaleelements, also in inches, were 0.050 in depth, 0.055 wide at the top,and about 0.015 wide at the bottom, which was rounded. The sidewallslope of, the female embossing elements was about 65° . As thephotographs clearly show, the effect of using unmatched embossingelements has a variable effect on the web on a micro scale. However, acommon effect is the compression or shear of the web at some point alongthe sidewall of the male embossing element where it approaches contactwith the sidewall of the female embossing element. The differingsidewall slopes of the two elements prevent complete engagement andcause the web to be pinched off at some point while being virtuallyuncompressed at bottom of the male element. For this to occurconsistently it is preferred that the maximum width of the maleembossing element be at least as great as the maximum width of thefemale embossing element. Although not shown in these photographs, therelative positions of any given male and female embossing elements alsochange with time as the embossing elements of the two rolls or sleevesrotate in and out of engagement. Hence, in FIG. 4A for example, thereapparently was initial contact between the male and female embossingelements on the left side prior to the photograph being taken (note thecompression of the web at the top of the female embossing element leftsidewall). Hence, when interpreting these photographs, one must not onlytake into account the imperfections of the laser engraving process, butalso the dynamics (rolling action) of the embossing process.

FIGS. 5A and 5B are cross-sectional photographs (magnified 20×) of aconventional embossed product and a product in accordance with thisinvention, respectively, using the embossing pattern illustrated in FIG.9. Shown in FIG. 5A is a conventional single ply embossed creped tissuewhich has been embossed between a steel roll and a rubber roll. FIG. 5Bshows a like web embossed using laser engraved rubber rolls havingunmatched male and female embossing elements in accordance with thisinvention. Note the greater distinctness of the embossment in FIG. 5Bdue to the more sharply angled sidewalls. Also note the relativethickness of the two webs in the area of the edge of the embossments. Inthe web of FIG. 5B, this area is significantly thinner than the otherareas along the sidewalls of the embossment. In contrast, thecorresponding areas of the conventional embossment of FIG. 5A are nothinner than the other areas-along the embossment sidewalls. This occursthroughout the entire web. It is theorized that applying maximumcompression and/or shear only at the edge of the embossment realigns ordeforms the fibers in this area in such a manner to give the resultingembossment greater structural integrity. In effect a permanent crease orbend is imparted to the web at the edge of the embossment which resultsin greater embossment distinctness and a greater firmness retention forthe embossed web.

FIG. 6 illustrates the apparatus used to measure the Firmness Index forroll products. The apparatus is available from B.C. Ames Company,Waltham, Mass. 02154 and is known as an Ames #16 Bench Comparator. Shownis a roll product 50 being measured which is supported on a core shaft51, which in turn is supported by a suitable stand 52. A dial indicator53 (#3223 long range indicator having a 3 inch range) mounted on thecomparator stand displays the distance of travel of the probe rod 54 anddisplays readings from 0-100 in increments of 0.001. The length of thepost 55 of the comparator stand is 15 inches long. The tip of the proberod is fitted with a contact point 56 having a 13/64 inch diameter and a11/64 inch radius of curvature (Model P-100 Ames contact point). Theprobe rod is adapted to be loaded with slotted weight discs 57 to varythe load and resulting travel of the probe rod in deflecting the surfaceof the product. The total downward force exerted by the probe rod, whenunloaded is between 70-80 grams.

When carrying out the Firmness Index procedure, the roll product isplaced on the core shaft and holder so the indicator probe isapproximately centered on the roll, end to end, and hits the apex of theroll curvature. The indicator probe is gently lowered onto the surfacecrown of the roll and the height of the dial indicator is adjusted untilthe reading on the dial indicator falls between 1.5 and 1.9 inches. Theproduct roll is then rotated to a different center position and the dialindicator reading is recorded after the probe rod has been in contactwith the product roll for 15 seconds. This is the first reading. Then,with one hand, the indicator probe is firmly grasped with the thumb andforefinger above the indicator, dial using the dial housing for support.With the other hand, a 1 pound weight disc is placed on the indicatorprobe. The indicator probe is then gently lowered onto the sample rollsurface. After the indicator probe has been in contact with the productroll for 15 seconds, the dial indicator reading is taken. This is thesecond reading. Subtract the second reading from the first reading. Thedifference is a measure of the roll firmness. Repeat the foregoingprocedure at two random positions around the circumference of theproduct roll, each position being a fixed distance from each end of theroll. For bath tissue, the second and third readings should be one inchfrom the roll edges. For paper towels, the second and third readingsshould be two inches from the roll edges. The average of the threereadings is the Firmness Index for the product.

FIG. 7 illustrates the apparatus used to measure the Firmness Index forproducts comprising a stack of webs 58, which is very similar to theapparatus described in regard to FIG. 6. The only difference from theapparatus illustrated in FIG. 6 is the elimination of the core shaft forsupporting the product sample to be measured. Instead, for productscomprising a stack of webs, the product stack is simply placed on asuitable tray support 59 or other suitable means which supports thecorners of the stack and rests on base of the test apparatus. In mostinstances the probe rod will be long enough to reach the stack. If not,the product stack can be further supported by any suitable means whichraises the stack sufficiently to be measured.

The procedure for determining the Firmness Index for a stack of webs isthe same as that described above with regard to roll products, exceptthat the three measurements to be averaged are taken at differentlocations. The first measurement is taken at the center of the product,as viewed from above. The second and third measurements are taken atdiametrically opposite corners of the product, one inch from both edgeswhich form the chosen corner. As before, the average of the threemeasurements is the Firmness Index for the product stack.

The relationship of roll Firmness Index and roll Bulk for two differentembossed webs is illustrated in FIGS. 8A and 8B, in each casegraphically illustrating a significant advantage of this inventioncompared to conventional embossing. The plot of FIG. 8A represents acomparison of a throughdried tissue web which was embossed by matchedsteel embossing rolls on the one hand and, on the other hand, by laserengraved rubber embossing rolls in accordance with this invention. Theembossing pattern for both pairs of embossing rolls was the butterflypattern illustrated in FIG. 9. The basesheet was a one ply, throughdriedweb having a basis weight of 33 grams per square meter and a geometricmean tensile strength of about 1300 grams per 3 inches of width. Thefurnish was a homogeneous mixture of 60 weight percent softwood bleachedkraft and 40 weight percent hardwood bleached kraft papermaking fibers.The matched steel embossing roll elements appeared in cross-section asillustrated in FIG. 1 and had a depth of 0.042 inch, a base width of0.067 inch, and an apex width of 0.025 inch. The laser engravedembossing roll elements appeared in cross-section as illustrated in FIG.4 and had dimensions set forth in the description of FIG. 4. In eachcase, a 16 inch wide roll of the basesheet material was unwound,embossed at three different embossing levels, perforated every 41/2inches to define individual sheets, and wound onto a 1 5/8 inch diametercore to form a log having a 300 sheet count. The log was then cut with aband saw into three product rolls of single-ply bath tissue. For thematched steel embossing, the three different levels of embossing wereobtained by three different levels of engagement of the embossingelements: 0.015 inch, 0.020 inch, and 0.024 inch off bottom. For thelaser engraved embossing, the three different levels of embossing wereobtained by placing shims between the embossing roll bearing housingsand increasing the spacing by 0.005 inch at a time. The initial settingwas subjectively determined to give relatively heavy embossing. Afterthe basesheet was embossed at all three conditions, the procedure wasreplicated to obtain two data points for each condition to improve theconfidence level of the data. The results are plotted in FIG. 8A.

FIG. 8B is a similar plot, but for a different basesheet. The basesheetused for this plot was a wet pressed, two-ply tissue web having acombined basis weight of 31 grams per square meter and,a geometric meantensile strength of about 1100 grams. The furnish was a homogeneousblend of hardwood, softwood, bagasse and secondary papermaking fibers.The procedure and the embossing rolls were otherwise as described abovewith respect to FIG. 8A, except that only two levels of embossingelement engagement were tested for the matched steel embossing: 0.016inch and 0.013 inch. The laser engraved embossing rolls were adjustedonce by 0.005 inch using shims as described above.

As is illustrated by both plots, as the Bulk is increased the FirmnessIndex increases for the matched steel product. (An increasing FirmnessIndex means decreasing firmness.) For the products of this invention,however, the Firmness Index remained relatively constant as the Bulk wasincreased. Hence by utilizing the method of this invention, one canincrease roll Bulk while maintaining a desireable level of rollfirmness. At the same time, a more distinct, well-defined embossingpattern is obtained.

It will be appreciated that the foregoing description and examples,given for purposes of illustration, are not to be construed as limitingthe scope of this invention, which is intended to include allequivalents thereto.

We claim:
 1. An embossing apparatus for embossing a tissue sheetcomprising first and second rotatable embossing rolls positionedparallel to each other, said first roll having a plurality of maleembossing elements having angled sidewall slopes and said second rollhaving a plurality of female embossing elements having angled sidewallslopes, wherein the male and female embossing elements intermesh witheach other as the rolls are rotated, wherein the sidewall slopes of theintermeshing male and female embossing elements differ from each other,and wherein the sidewall slopes of the male and female embossingelements are irregular in cross-section.